1. Field of the Invention
This invention relates to a core orientation device for determining the orientation of core samples taken during a drilling process.
The apparatus allows one to obtain a diamond drilled core sample from the foot or bottom of a drilled hole, which can subsequently be repositioned in relation to its original attitude in the strata or formation as it was located prior to being "cored." This is done by establishing the dip of the bore hole, as well as the angular orientation of the core sample with respect to the bore hole axis. This latter involves establishing not only the orientation of the core tube, which holds the core sample, but also the orientation of the core sample itself with respect to the core tube.
"Wire line" drilling is the system of drilling most commonly used today. In wire line drilling, a string of rods made up of ten foot lengths of flush-threaded tubing is introduced into the bore hole. At the bottom or beginning of the rod string is an outer core barrel. Fastened to the bottom of the core barrel is a core bit which cuts a cylindrical core as it penetrates the formation.
As the core is produced it passes through the centre of the coring bit and enters the inner core barrel or core tube. The core tube remains stationary in relation to the core being produced as the bit revolves and penetrates the formation. This is accomplished by virtue of a set of bearings at the top of the core tube. The core tube is held in place by a set of latches locked into a locking coupling, at the top or back end of the core barrel. At the bottom of the core tube, which is located slightly behind the face of the coring bit, is a device called a core lifter. This unit contains a core spring which slips over the core as it is entering the core tube.
When the core tube has been filled, the drill is stopped and the rod string is pulled slightly. At this point the core spring grabs the core and breaks it from the bottom of the hole. The core then remains locked in the core tube. A device called an overshot is then lowered through the centre of the rod string on a small cable or "wire line". The overshot is lowered to a point where it latches onto the back or upper end of the core tube. This connection releases the set of latches of the locking coupling, which hold the core tube in place while the core is produced, and the tube is pulled to surface.
Without instrumentation, the only way to determine the inclination of geological formations in any hole is by drilling additional holes on either side of the first hole. This means that the formation will be intersected at either a higher or lower depth than in the first hole, or possibly not at all. A total of three holes, minimum, are required to interpret the direction of the bedding angle. The cost of drilling additional holes is high.
2. Description of the Prior Art
Accordingly, a number of instruments have been developed to provide information about the orientation of the sample. Some examples are found in the following U.S. Pat. Nos.: 2,650,069; 2,657,013; 2,707,617; 2,859,938; 3,032,127; 3,059,707; 3,363,703; 3,964,555; 4,128,134; 4,334,429; 4,311,201 and 4,542,648.
The above systems are generally quite complicated, and are aimed at orienting the sample with respect to the core tube the earth's strata. For orienting the core tube with respect to the hole, various means such as camera systems have also been used. U.S. Pat. No. 2,974,739, for example, shows the combination of a gun unit mounted in a core barrel adapted to fire missile into the rock to be cored, for marking the core, and a recording well unit including a camera to photograph shadows of a survey instrument. U.S. Pat. No. 3,450,216 discloses a core orienting apparatus including a multiple-shot camera and means to continually make groove marks along the length of a core.
In general, the above prior art systems suffer to varying degrees from various deficiencies, including complexity, cost, and unreliability.